SEOUL, South Korea — Defying weeks of international warnings of more censure and further sanctions, North Korea launched a rocket on Friday, an act that the United States called a cover for developing an intercontinental ballistic missile that one day might be able to carry a nuclear warhead. But the three-stage rocket appeared to break up and collapse moments after the launching.

Officials from the United States, South Korea and Japan called the launching a failure, and the Japanese government said the rocket had disintegrated into several pieces while still in North Korean territory or over South Korean waters.

“We believe that the rocket fell apart in several pieces and plunged several minutes after the takeoff,” said Kim Min-seok, a spokesman for South Korea’s Defense Ministry. He said the assessment of both South Korean and American intelligence monitors was that “the North Korean missile launching has failed.”

The rocket, called the Unha-3, blasted off from the Soehae launching site near North Korea’s western border with China, about 7:40 a.m., the South Korean Defense Ministry spokesman said.